This invention relates generally to meters for use by underwater divers and, more particularly, to an electronic apparatus for recording and displaying time/depth data. Although the invention has particular application to sport and recreational diving, it may also be used by other types of divers (commercial, military, scientific and research, etc.) as will become readily apparent hereinbelow.
Of special concern for sport and recreational divers is the accurate recording of the depth of the dive and duration of that dive in order to avoid decompression sickness or the "bends". Additionally, that information must be retained and recalled for appropriate computation if a second or succeeding dives are performed within a twelve hour period of the first dive.
Over the years, the U.S. Navy has developed a set of guidelines for use by the diver so he can plan his dive and avoid the onset of decompression sickness. These guidelines are known as the U.S. Navy Air Decompression Tables or, more commonly, the "tables". Most authorities agree that the tables provide the best guidelines for safe diving by sport divers and avoidance of decompression sickness.
A typical single dive by a sport diver may involve excursions to various depths for various periods of time. According to the tables, the depth of any such dive is the deepest point of that dive and the time of the dive or "bottom time" is calculated from the beginning of the initial descent to the time of an uninterrupted ascent directly to the surface. In order to properly use the tables, then, it is essential that the diver have this information for each and every dive. In addition, proper use of the tables requires that the diver ascend to the surface at a rate of 60 feet per minute.
Current practice in the sport diving community is to provide this essential information by use of a depth gauge and a separate watch or timer. This simultaneous monitoring of two information sources is both difficult in practice and highly subject to erroneous readings and subsequent erroneous calculations by the diver. Additionally, state of the art depth gauges do not provide a retained indication of the maximum depth of the dive; the diver must simply remember the maximum depth attained.
The present invention provides a significant advance in the art in the form of an electronic depth/time recording and displaying instrument which records and displays the following critical information for the diver:
(a) maximum depth attained; PA1 (b) bottom time; PA1 (c) existing depth at any point in the dive; PA1 (d) elapsed time of the dive from initial descent to time of ascent; and PA1 (e) ascent time, to within two feet of the surface. PA1 (a) surface time after the dive up to 12 hours or until the invention is reset for a repetitive dive; p1 (b) low battery condition; PA1 (c) lighted display of all readouts; and PA1 (d) flashing, warning display indicating the instrument's limits have been exceeded.
In addition, the invention further displays the following critical information:
The basic components of the system are both simple and reliable. First, an otherwise conventional Bourdon tube or a novel bellows assembly herein disclosed and claimed continuously monitors ambient pressure and changes therein. An otherwise state of the art microprocessor receives sensed data and computes the depth and elapsed time parameters of the dive. The sensed data is relayed to the microprocessor by a novel, direct digital input and tracking system herein disclosed and claimed which provides the attendant advantages of simplicity and accuracy without need of any analog to digital conversion of data or thus any components and structure to accomplish such conversion.
The following eight prior patents are representative of the present state of the art in the field of the instantly disclosed and claimed invention.
U.S. Pat. No. 2,037,879 issued to Chalatow discloses a Bourdon tube 22 for sensing pressure and having a pivoted control arm 23 at an end thereof which wipes across a series of contacts to generate downstream impules to eventually provide perceived, useful information. Similar teachings appear in U.S. Pat. Nos. 576,208 issued to Lozier and 774,815 issued to Anderson, although in the latter instance at least, the wiped surface is essentially a rheostat. Another Bourdon tube-transducer apparatus is shown in U.S. Pat. No. 3,599,493 issued to Thomas and U.S. Pat. No. 3,593,582 issued to Birkmeyer discloses a bellows tube which expands to close contacts 80, 56 to generate a signal.
The following prior patents are more relevant to the field of underwater diving. U.S. Pat. No. 3,670,575 issued to Emerick discloses a system for reading tank pressure decay and produce a time-left indication for the diver. Other, less relevant disclosures of watch/depth meter combinations are disclosed in U.S. Pat. Nos. 3,377,860 issued to Masters and 3,696,610 issued to Charbonnier.
A popular device known as the "decompression meter" or simply the "meter" has been marketed by Scubapro of Compton, Calif. for years and is disclosed and claimed in U.S. Pat. No. 3,121,333 issued to Alinari. The "meter", however, includes no electronic circuitry. Rather, it is an uncomplicated analog device which gives a more or less reliable indication of the degree of nitrogen gas load in the diver's body. No watch or time elapsed device is incorporated in the "meter".
More recently, Dacor Corporation of Northfield, Ill. has announced plans to market a dive computer which combines a variety of devices including a depth gauge, a watch and a computer programmed to utilize the U.S. Navy Air Decompression Tables. LED readouts are provided thus requiring a rather substantial power source and a pressure transducer is employed to provide pressure information for the circuitry and microprocessor or computer. Up to ten readouts are provided, which may confuse the diver and, due to power requirements, only a 10% on-time is provided, meaning the diver will spend most of his dive without any information.
Conversely, the present invention provides an accurate and reliable dive timer or watch and depth gauge which is conveniently packaged in a small case about the size of a present day depth gauge and thus is easily worn on the wrist. Power requirements are minimal and LCD readouts are provided so the diver has constant, updated information. The U.S. Navy Air Tables are not built into the instrument; rather, reliable and accurate time of dive and maximum depth information is provided the diver and retained in the instrument so the diver may easily calculate his repetitive dive profile. In place of a pressure transducer, the accuracy and realiability of which are at least questionable, a novel, pressure sensitive bellows assembly is provided with a plurality of wipers or fingers tracked across a patterned (e.g., photo-etched) substrate for direct digital input of pressure information to a small microprocessor or computer without need of any analog to digital data conversion. The instrument is rather uncomplicated in structure and thus reliable in service.